Scanning tunneling microscopes (STM) and scanning-force microscopes (SFM, AFM) are used for characterizing surface morphology in research, teaching, and industry.
The scanning tunneling microscope and scanning-force microscope are based on the principle of scanning a surface using a fine tip or scanning needle that is attached to a cylindrically tubular piezoelectric moving element. For a scanning tunneling microscope, the current is measured between the tip and the sample over the surface of a sample to be analyzed.
For a scanning-force microscope, instead of the scanning needle a lever, also referred to as a cantilever, is attached. In this case the force between the sample and the cantilever is used as the measurement variable.
A micromanipulator is known from DE 3610540 C2 [U.S. Pat. No. 4,785,177] for the micromovement of objects in the X-, Y-, and Z-directions, the object being supported on at least three cylindrically tubular piezoelectric moving elements. The moving elements have a closed, electrically conductive inner coating as well as multiple mutually insulated partial coatings on the exterior. By application of an electrical voltage between individual partial coatings and the inner coating, depending on the polarity the cylindrically tubular piezoelectric moving elements are caused to bend or deform in the X-, Y-, and Z-directions.
These motions are very precise, and are referred to below as “fine motions.” Continuous motions may be performed with a precision as great as one-thousandth of a nanometer. In contrast, movement in a range of only several micrometers can be achieved by deformation of the piezo elements.
An inertial drive is used for coarse motion of an object or object holder. When the moving elements are appropriately actuated, for example by a sawtooth pulse, the object or object holder to be examined undergoes a change in position as the result of the inertia of the object or object holder. This motion is referred to below as “coarse motion,” and spans the region of several nanometers to several millimeters. The coarse motion does not occur continuously as for the fine motion, but instead occurs in steps in the nanometer range, the width of which is specified by the amplitude of the sawtooth pulse. By means of coarse motions resulting from the inertial drive, it is possible to achieve straight-line motions in the X- and Y-directions for displacement of the position of an object or object holder relative to a sample to be examined.
In the discussion below, “micromotion” refers to both fine and coarse motions.
It is known from DE 38 44 659 C2 [U.S. Pat. No. 5,325,010] that in an axial, vertical orientation of the nanomanipulator the moving elements support an obliquely or helically extending support surface. The helically extending support surface may be divided into multiple uniform sections, at least one cylindrically tubular moving element supporting each section.
When the cylindrically tubular moving elements are appropriately actuated, the helically extending support surface is set into rotation. This results in a coarse motion of the treating or analyzing plane in the axial direction (Z-direction) as well.
The displacement exceeds that which would be achievable by application of an electrical voltage to the piezo element itself. By use of this method it is possible, for example, to roughly move a tip or scanning needle to the sample.
When the moving elements are appropriately actuated or moved in another manner, the support surface may undergo a horizontal coarse motion in the X- or Y-direction. If the object is brought into an appropriate position by the coarse motions in the X-, Y-, and Z-directions, an additional, more precise motion (fine motion) may be achieved by deformation of a cylindrically tubular piezo element by use of a scanning needle.
Micromanipulators are equipped with scanning needles for the above-mentioned purpose in order to analyze or treat an object or sample. The scanning needle is attached to a cylindrically tubular moving element. The piezoelectric effect causes the moving element to be deformed or bent, resulting in the desired relative motion between the scanning needle and the object (fine motion).
The aim of measuring the electronic characteristics and charge movement through nanostructures is achieved by changing from microelectronics to nanoelectronics.
From Shiraki et al (I. Shiraki, F. Tanabe, R. Hobara, T. Nagao, and S. Hasegawa, 2001, “Independently driven four-tip probes for conductivity measurements in ultrahigh vacuum,” Surf. Sci. 493, 633-643) a four-probe system is known that is provided in a UHV SEM. Each probe represents a S™. The SEM is used to control the manipulation of the probes, and allows the probes to be localized. By rough positioning the probes are brought to within a few μm of one another. Cylindrically tubular moving elements having five electrodes each allow the probes to be positioned with precision, and move same in the nanometer range, thereby performing fine positioning of the probes. Electrical characteristics of components may be analyzed by use of, for example, four probes or scanning needles.
Also known from the prior art is a UHV nanoprobe. These allow a multipoint measurement to be carried out on semiconductors and biomolecular components, for example, down to the nanometer range. To this end, four scanning needles are brought to within approximately 600 nanometers of one another, and the conductivity of the component is independently measured between the scanning needles. The scanning needles may be independently positioned via appropriate coarse and fine manipulation.
A disadvantage of all the manipulators known heretofore is that a complicated mechanism is essential for the damping of vibrations.
Vibrations from the surroundings of the manipulator interfere with the ability to position the scanning needle and with the localization thereof using SEM, TEM, or comparable methods. For example, in the positioning of probes, vibrations resulting from ventilation units must be compensated for or damped.
It has been proposed to provide the tips, the object support, and all other devices that are necessary for positioning and localizing the tips or the sample, on an air-cushioned platform. Pneumatic automatic vibration dampers are also known from the prior art. The smaller the distance between the scanning needles and/or to the sample, the greater the effort required for suppressing such vibrations. For this reason the manipulators are costly.